1. Cryo-EM reveals the conformational epitope of human monoclonal antibody PAM1.4 broadly reacting with polymorphic malarial protein VAR2CSA.
- Author
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Raghavan, Sai Sundar Rajan, Dagil, Robert, Lopez-Perez, Mary, Conrad, Julian, Bassi, Maria Rosaria, Quintana, Maria del Pilar, Choudhary, Swati, Gustavsson, Tobias, Wang, Yong, Gourdon, Pontus, Ofori, Michael Fokuo, Christensen, Sebastian Boje, Minja, Daniel Thomas Remias, Schmiegelow, Christentze, Nielsen, Morten Agertoug, Barfod, Lea, Hviid, Lars, Salanti, Ali, Lavstsen, Thomas, and Wang, Kaituo
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MONOCLONAL antibodies ,ERYTHROCYTE membranes ,ERYTHROCYTES ,MEMBRANE proteins ,CELL-mediated cytotoxicity - Abstract
Malaria during pregnancy is a major global health problem caused by infection with Plasmodium falciparum parasites. Severe effects arise from the accumulation of infected erythrocytes in the placenta. Here, erythrocytes infected by late blood-stage parasites adhere to placental chondroitin sulphate A (CS) via VAR2CSA-type P. falciparum erythrocyte membrane protein 1 (PfEMP1) adhesion proteins. Immunity to placental malaria is acquired through exposure and mediated through antibodies to VAR2CSA. Through evolution, the VAR2CSA proteins have diversified in sequence to escape immune recognition but retained their overall macromolecular structure to maintain CS binding affinity. This structural conservation may also have allowed development of broadly reactive antibodies to VAR2CSA in immune women. Here we show the negative stain and cryo-EM structure of the only known broadly reactive human monoclonal antibody, PAM1.4, in complex with VAR2CSA. The data shows how PAM1.4's broad VAR2CSA reactivity is achieved through interactions with multiple conserved residues of different sub-domains forming conformational epitope distant from the CS binding site on the VAR2CSA core structure. Thus, while PAM1.4 may represent a class of antibodies mediating placental malaria immunity by inducing phagocytosis or NK cell-mediated cytotoxicity, it is likely that broadly CS binding-inhibitory antibodies target other epitopes at the CS binding site. Insights on both types of broadly reactive monoclonal antibodies may aid the development of a vaccine against placental malaria. Author summary: Placental malaria remains a major global health problem. The disease is caused by the accumulation of malaria parasite-infected red blood cells in the placenta. The parasites export members of the polymorphic VAR2CSA protein family onto the red blood cell surface to bind placental chondroitin sulphate A (CS). The VAR2CSA protein family have diversified in sequence to avoid immune recognition, but recent CryoEM structures of VAR2CSA shows that all variants fold into a large, dense and stable core comprised of multiple interwoven "DBL" domains, and a flexible two-DBL domain tail. Immunity to placental malaria is acquired through exposure and thought to be mediated by broadly reactive antibodies acting through neutralizing CS binding or opsonizing infected red blood cells for cell-mediated killing. Here, we used negative stain and cryo-EM to resolve the first molecular structure of a broadly reactive antibody (PAM1.4) against VAR2CSA. We find that the antibody binds a highly conserved conformational epitope on the VAR2CSA core structure, distant from previously determined CS binding sites. This aligns with new data showing negligible PAM1.4 neutralization of parasite binding to CSA. As a well-characterized non-neutralizing monoclonal antibody, PAM1.4 and Fc-modifications thereof, can now be used for reference and benchmarking in future studies aiming to map, identify and qualify functional antibodies against VAR2CSA in the continued quest for vaccines or therapeutics against placental malaria. [ABSTRACT FROM AUTHOR]
- Published
- 2022
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